1. Field of the Invention
The present invention relates to an optical disc player, and more particularly, to an optical disc player which compensates for eccentricity components regardless of the playback speed of an optical disc.
2. Description of the Related Art
Generally, compact disc players (CDP) or digital video disc players (DVDP) emit laser on the track of a disc, pick up a reflected ray and read information contained in the reflected ray that has been picked up. The disc has a plurality of spiral tracks, and pits having information data are contained in each track. The laser reads the information while following the spiral tracks.
Eccentricity may result in the event that the tracks are not manufactured in the structure of a concentric circle or if the central axis of a spindle motor rotating the disc is altered. A laser beam may deviate from the tracks when following the tracks to read information if the eccentricity deviates from the error tolerance range of an optical disc player.
FIG. 1 shows an example of a conventional optical disc player. Referring to FIG. 1, the conventional optical disc player includes an optical disc 10, a pickup 20, a radio frequency (RF) amplifier 50, a focusing servo 60, a tracking servo 70, a spindle controller 80 and a compensating circuit 100.
FIG. 2 shows another example of a conventional optical disc player. Referring to FIG. 2, the conventional optical disc player includes the optical disc 10, the pickup 20, the RF amplifier 50, the focusing servo 60, the tracking servo 70, the spindle controller 80 and the compensating circuit 100.
Eccentricity compensation in the conventional optical disc players is performed in accordance with the following. In FIG. 1, an eccentricity compensator 130 detects an eccentricity from the output signal of the tracking servo 70, and an adder 120 combines the output signal of the tracking servo 70 with a signal which compensates for the detected eccentricity. The signal output from the adder 120, i.e., the signal compensated for the eccentricity, controls a tracking actuator 40 in the pickup 20.
In FIG. 2, the eccentricity compensator 130 extracts an eccentricity from the output signal of the RF amplifier 50, and the output signal of the RF amplifier 50 is combined in the adder 120 with a signal from the eccentricity compensator 130 which compensates for the eccentricity. The signal output in the adder 120, i.e., the signal compensated for the eccentricity, controls the tracking actuator 40 in the pickup 20, via the tracking servo 70.
The conventional optical disc players shown in FIGS. 1 and 2 compensate for the eccentricity at the very place where the eccentricity is extracted, i.e., the output end of the tracking servo 70 (FIG. 1) and the output end of the RF amplifier 50 (FIG. 2).
A tracking filter (not shown), which is one of the elements constituting the tracking servo 70, outputs a signal having a phase delay. In the case of FIG. 1, the compensating circuit 100 has a disadvantage in that a phase delay included in an extracted eccentricity in the tracking filter must be considered. In FIG. 2, a signal, which is compensated in the compensating circuit 100 and then is transferred to the tracking actuator 40 via the tracking servo 70, causes phase delay when passing through the tracking servo 70, which results in incorrect eccentricity compensation.
FIG. 3 is a waveform diagram of signals related to eccentricity compensation in a conventional optical disc player. As can be seen in FIG. 3, a signal FG is the output signal of a disc rotation information detector 110, a signal TE is an actual eccentricity which is input into the eccentricity compensator 130 from the tracking servo 70 or the RF amplifier 50, a signal DE is an eccentricity extracted in accordance with the edge of the signal FG in the eccentricity compensator 130 and a signal EC which is compensated for eccentricity is the output signal of the adder 120.
In FIG. 3, the eccentricity compensation rendered in a conventional optical disc player compensates for eccentricity during the subsequent rotation of an optical disc by extracting eccentricity included in the output of the RF amplifier 50 or the tracking servo 70 at the edge of the output signal FG of the disc rotation information detector 110 and storing the extracted eccentricity in a memory. However, with regard to the compensated signal EC (which is indicated as TRD in FIGS. 1 and 2), the discontinuous points of an eccentricity, i.e., the portions corresponding to the edges of the signal FG, function as a high frequency component in the tracing servo 70 thereby preventing stable operation of the tracking actuator 40.
FIG. 4 is a waveform diagram of signals related to eccentricity compensation when changing the playback speed of a disc in a conventional optical disc player. Referring to FIG. 4, the signal FG is the output signal of the disc rotation information detector 110 and a signal ECC is an eccentricity to be compensated for. An eccentricity to be extracted and compensated at 32-times speed is difficult to be correctly compensated at 24-times speed or an even slower section where the eccentricity is too large.
To solve the above problems, it is an objective of the present invention to provide an optical disc player that solves phase delay by making the positions where an eccentricity error is extracted and compensated for different from each other and includes a pulse signal generator to produce a plurality of pulse signals corresponding to a signal FG changing according to the change of the playback speed of a disc.
Accordingly, to achieve the above objective, there is provided an optical disc player according to the present invention including a spindle controller, a pickup, a radio frequency (RF) amplifier, a focusing servo, a tracking servo and an eccentricity compensator. The spindle controller rotates an optical disc. The pickup has a focusing actuator and a tracking actuator and reads information recorded on the optical disc. The RF amplifier detects and amplifies a focusing error signal and a tracking error signal from information on the optical disc obtained from the pickup. The focusing servo controls the focusing actuator in response to the amplified focusing error signal. The tracking servo outputs a tracking control signal in response to the amplified tracking error signal. The eccentricity compensator outputs a signal which compensates for the eccentricity of an optical disc in response to the output signal of the spindle controller, the amplified tracking error signal and the amplified tracking control signal. The eccentricity compensator detects the rotation period of the optical disc, produces a plurality of pulses using the detected rotation period, detects an eccentricity included in the amplified tracking error signal according to the plurality of generated pulses and generates a compensating signal for the detected eccentricity. Also, the compensating signal automatically changes in relation to the playback speed of the optical disc.
In one embodiment, the eccentricity compensator includes a disc rotation detector, a pulse signal generator, an eccentricity controller, an eccentricity compensator and an adder. The disc rotation detector outputs a series of digital pulses every rotation of the optical disc in response to the output signal of the spindle controller. The pulse signal generator outputs first and second pulse signals in response to the series of digital pulses. The eccentricity controller outputs an eccentricity control signal which indicates whether the eccentricity of the optical disc is to be compensated for. The eccentricity compensator outputs an eccentricity compensation signal in response to the eccentricity control signal, the first pulse signal, the second pulse signal and the amplified tracking error signal. The adder combines the eccentricity compensation signal with the tracking control signal and transmits the combined result to the pickup.
In one embodiment, the first pulse signal is generated at the falling edge and rising edge of the received series of digital pulses, and a plurality of pulses are generated in the second pulse signal for each pulse of the first pulse signal.
In one embodiment, the eccentricity compensator includes a band-pass filer, an eccentricity extraction and compensation unit and a gain/phase controller. The band-pass filter receives the amplified tracking error signal and removes DC components or noise therefrom. The eccentricity extraction and compensation unit extracts and compensates for an eccentricity in response to the first pulse signal, the second pulse signal, the eccentricity control signal and the output signal of the band-pass filter. The gain/phase controller receives the output signal of the eccentricity extraction and compensation unit and regulates the gain of the received signal and the frequency thereof.
In one embodiment, the eccentricity extraction and compensation unit includes a one-rotation detector, a memory controller, a memory and an eccentricity compensation selector. The one-rotation detector outputs a one-rotation flag signal and an eccentricity compensating selection signal in response to the first pulse signal and the eccentricity control signal. The memory controller outputs an address signal and a read/write signal in response to the eccentricity control signal, the second pulse signal and the one-rotation flag signal. The memory stores an eccentricity error which is the output signal of the band-pass filer or outputs the stored eccentricity error in response to the second pulse signal, the address signal and the read/write signal. The eccentricity compensation selector selects the eccentricity error or a predetermined reference value according to the eccentricity compensation selection signal.
The one-rotation detector further receives a mute signal, mutes eccentricity compensation based on the mute signal, and maintains the phase of an eccentricity in preparation for the subsequent compensation.